Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
1999-03-08
2001-11-27
Solis, Erick (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S698000, C123S520000, C701S104000
Reexamination Certificate
active
06321735
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to fuel injection systems and evaporative emissions control systems used in automobile fuel systems to reduce evaporative and exhaust emissions and, in particular, to such systems in which the fuel calculations performed by the fuel injection system account for the fuel vapor added to the intake air during purging.
BACKGROUND OF THE INVENTION
The automotive industry has had notable success in the reduction of regulated gaseous emissions from the use of hydrocarbon fuels in mass produced automobiles. For gasoline spark ignited engines, the gaseous emissions fall into two categories:
(1) evaporative emissions—which relate to unburned fuel vapors escaping from the vehicle's fuel tank, and
(2) tailpipe emissions—which relate to emissions from the exhaust of the engine and include unburned and partially burned fuel, carbon monoxide, and oxides of nitrogen.
In the mid 1970s, catalytic converters and closed loop fuel control was adopted almost universally in the United States and progressively in other countries. As stricter emission control requirements were written into law, microprocessor-controlled fuel injection eventually became widespread, allowing for more elaborate and sophisticated control systems and fuel control strategies.
Early automotive control systems often used emulations of the mechanical controls that had been replaced by electronically-actuated devices. Simple physical and empirical strategies with primarily tabular calibrations were used in order to be compatible with the limited microprocessor capacity on-board the vehicle. Current state-of-the-art low emission systems utilize more advanced controls strategies that include mathematics and physics-based models of the complex chemical, thermodynamic, mechanical, and electrical processes that exist in the automobile. This modeling and control strategy is implemented using software which provides designers with a mix of advanced controls techniques and thrifty empiricism that they can use in providing efficient and effective engine control logic.
In state-of-the-art low emission gasoline vehicles, both evaporative emissions and tailpipe emissions have been reduced by more than 90% from previous uncontrolled levels. The reduction in evaporative emissions has been achieved largely by use of evaporative emission control systems that utilize a charcoal canister to store fuel vapors from the fuel tank, with periodic purging of the vapors into the air intake manifold of the engine where they are drawn into the engine cylinders and burned. However, the objective of further reducing the emissions to near zero levels gives rise to a conflict between the need for aggressive purging of the charcoal canister to control evaporative emissions and extremely precise control of engine Air/Fuel ratio for tailpipe emissions control. For example, the design of high pressure fuel injection systems has often included the use of high-flow re-circulation of fuel (pumped from the fuel tank to the engine and back to the tank). This would allow the fuel injectors to be maintained at lower operating temperatures, even in applications where underhood temperatures and fuel injector location would otherwise have resulted in excessive fuel injector temperatures. This has helped avoid phenomena such as vapor lock and is also considered desirable for the longevity and precision of the fuel injector. However, this fuel control approach is at odds with the need to keep tank temperatures low to avoid evaporative running losses in extreme conditions. In addition, new requirements for On-Board Refueling Vapor Recovery (ORVR), On-board Diagnostic (OBD II and EOBD) and real-time and high temperature evaporative emission testing have created a strong need to more capable purge strategies.
Traditionally, engine control systems have treated canister gases as a disturbance to the engine fueling and this often required compromise between the desire for improved evaporative emission control and the need for flawless driveability and fuel control in a variety of operating conditions and with a multiplicity of commercial fuels of varying quality. Steadily lower tailpipe emission requirements have made the more careful integration of vapor (purge) and liquid (fuel injector) delivery to the engine essential to robustly achieve the level of fuel control required for extremely low tailpipe emissions for both test cycle and real world conditions and fuels. Accordingly, engine control strategies have been proposed in which the calculation of the injector fuel quantity takes into account the quantity of purge fuel contained in the intake air ingested into the cylinder. See, for example, U.S. Pat. No. 5,596,972 to Sultan et al. In the Sultan et al. system, a physical hydrocarbon sensor is used to determine the concentration of fuel vapors in the purge gas and this estimate of the purge fuel vapor is used to determine the quantity of fuel to be delivered by the injector and to control the flow rate of purge gas into the intake manifold.
SUMMARY OF THE INVENTION
The present invention provides a fuel control system method and apparatus which estimates the fuel received from purging of an evaporative emission control system and accounts for this purge fuel in determining the amount of fuel to be injected. The fuel control system comprises both the evaporative emission control system and a fuel injection system. The fuel injection system includes an electronic control module (ECM), a mass airflow meter, idle air control valve, throttle position sensor, manifold absolute pressure (MAP) sensor, engine speed sensor, solenoid-operated fuel injector, and exhaust gas oxygen (O
2
) sensor. The evaporative emission control system includes the ECM as well as a charcoal canister, canister vent valve, purge valve, fuel tank pressure sensor, and a fuel tank temperature sensor. The ECM operates under program control to determine the amount of fuel to be delivered by a fuel injector to the cylinder of an automotive or other internal combustion engine. The ECM also operates the purge valve to control purging of the charcoal canister and the engine's fuel tank.
In accordance with one aspect of the invention, there is provided a method for determining the concentration of fuel vapor contained in purge gas inducted into a cylinder of the engine during purging of the evaporative emission control system. The method includes the steps of:
obtaining a data value representative of the concentration of purge fuel vapors in the purge gas,
operating a purge valve to permit the purge gas to be drawn into the cylinder of the internal combustion engine,
determining an additional amount of fuel to be injected into the cylinder using the data value,
injecting the additional fuel into the cylinder, and
adjusting the data value if the total amount of fuel provided to the cylinder is greater than or less than a desired amount of fuel.
The data value can represent the hydrocarbon concentration [HC] of the purge gas and, preferably, the adjusting step further comprises determining an error related to the difference between the total amount of fuel and the desired amount of fuel, and adjusting the data value using the error. The error can be determined using a measurement of the exhaust gases produced by combustion of the purge fuel and injected fuel. Separate hydrocarbon concentration estimates can be maintained for both the purge gas from the charcoal canister and the purge gas from the tank.
In accordance with another aspect of the present invention, the hydrocarbon concentration is updated iteratively during purge while closed loop corrections used in the fuel calculation are updated during periods when no purging occurs. This allows the closed loop corrections to be updated based on feedback that does not contain any purge-related error. As a result, the system avoids the large, erratic variations in the closed loop corrections that are seen in conventional fuel delivery systems.
In accordance with another aspect of the present invention,
Grieve Malcolm James
Himes Edward George
Qiao Ningsheng
Cichosz Vincent A.
Delphi Technologies Inc.
Solis Erick
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