Internal-combustion engines – Charge forming device – Air/fuel ratio prior to combustion responsive means
Utility Patent
1999-01-15
2001-01-02
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Air/fuel ratio prior to combustion responsive means
C123S674000, C123S320000, C701S103000
Utility Patent
active
06167877
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to evaporative emission control systems for automotive vehicles and, more particularly, to a method of compensating for purge vapors from an evaporative emission control system for an automotive vehicle.
2. Discussion
Modern automotive vehicles typically include a fuel tank and an evaporative emission control system that collects volatile fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing an activated charcoal mixture, to collect and store volatile fuel vapors. Normally, the canister collects volatile fuel vapors which accumulate during refueling of the automotive vehicle or from evaporation of the fuel. The evaporative emission control system also includes a purge valve placed between an intake manifold of an engine of the automotive vehicle and the canister. At certain times conducive to purging, the purge valve is opened by an engine control unit an amount determined by the engine control unit to purge the canister, i.e., the collected volatile fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within a combustion chamber of the engine.
As one skilled in the art will appreciate, the entry of purge vapors into the combustion chambers of the engine change the combustion characteristics of the engine. More particularly, the presence of purge vapors in the intake manifold change the required amount of fuel injected from the fuel injectors to maintain optimum drivability. Injecting too much fuel in the presence of the purge vapors causes an improper fuel to air ratio which may result in incomplete combustion, rough engine operation and poor emissions.
Although prior art methods of accounting for purged volatile fuel vapors from the evaporative emission control system have achieved favorable results, there is room for improvement in the art. For instance, it would be desirable to provide a method of identifying the source of the vapors from within the evaporative emission control system based on source characteristics, anticipating variations in the level of purge vapors using learned information from the identified source, and adjusting the amount of fuel delivered from the fuel injectors in accordance with the variations and sources of the purge vapors to maintain a desired fuel to air ratio.
SUMMARY OF THE INVENTION
It is, therefore, one object of the present invention to provide a method of accounting for purge vapors in an evaporative emission control system of an automotive vehicle.
It is another object of the present invention to provide a method of learning the concentration of purge vapor, identifying the source of the purge vapor, and predicting variations in purge vapor concentrations as a function of purge flow.
It is yet another object of the present invention to provide a method of identifying the appropriate time to initiate a purge cycle, providing the appropriate flow conditions such that the concentration of purge vapor can be learned, and controlling the purge flow rate such that purge vapors are depleted from the system.
It is still yet another object of the present invention to provide a method for predicting the concentration of purge vapor at the purge valve of the evaporative emission control system as a function of purge flow and accumulated flow through the canister.
It is another object of the present invention to provide a method of learning changes in the mass of the canister such that a mass of purge vapor in the canister can be determined.
It is yet another object of the present invention to provide a method of learning the flow rate of purge vapors from the fuel tank such that the fuel delivered through the injectors can be controlled under varying air flow and purge flow conditions.
It is still yet another object of the present invention to provide a method of accounting for a predictable purge vapor surge from the canister to provide improved fuel to air control and emissions results.
It is another object of the present invention to provide a method of learning the distribution of purge vapors within the engine manifold such that the amount of fuel delivered from various injectors can be selectively controlled to accommodate the purge vapor at that location of the engine.
To achieve the foregoing objects, the present invention provides a method of accounting for purge vapors in an evaporative emission control system of an automotive vehicle. The method includes a purge compensation model for identifying the concentration of purge vapor entering the intake manifold of the engine, identifying the source of the vapor as from the vapor collection canister or the fuel tank, and using this information to predict variations in vapor concentrations as a function of purge flow. Preferably, predicting variations in vapor concentrations is accomplished by using a physical model of the mass of air flow through the purge valve (based on air density). The mass of air flow is then modified based on the density of hydrocarbon for the learned concentration of purge vapors in the system. The method also includes a purge control model which uses mode logic to identify an appropriate time to initiate a purge cycle, provides the flow conditions necessary for a learning portion of the purge compensation model and increases purge flow rates after the learning is complete to deplete the contents of the canister. The purge control model also manages the time spent with purge active (learning purge) and purge inactive (learning volumetric efficiency or EGR). Preferably, the mode logic initiates a sequence of purge-active/purge-inactive cycles based on the learned parameters of the system through oxygen-sensor feedback. The following sequence is performed to learn the required parameters: a) learn the volumetric efficiency of the engine; b) learn the concentration and stability of the purge vapor during a low flow condition to identify a level of canister loading; c) increase purge flow through the purge valve using the learned canister information and learn deviations from a canister surface (i.e., model) as a function of tank flow; and d) repeat (a) and (c) indefinitely for the remainder of the drive.
As described in greater detail below, the present invention characterizes purge valve flow by using a surface for determining air mass flow rate as a function of vacuum at the purge valve and purge valve current. The flow through the valve is used to compute instantaneous flow rate and accumulated flow rate. A tactical adaption routine provides short term purge compensation (i.e., a tactical error term) through use of oxygen sensor feedback using proportional-integral control on an oxygen sensor integral error to tactically account for the purge concentration at the intake manifold. This term eventually forms the basis for all learning within the purge system.
The tactical adaption routine allows the system to maintain control and stability in the oxygen sensor feedback part of the methodology by extracting the integral error and learning it as representing purge concentration. By regulating the learning rate of the tactical adaption routine (O
2
rate/10) and a strategic adaption routine described below (O
2
rate/100), the learning of a quasi-steady state purge vapor concentration is made possible. Also, due to the controlled learning rate, the ability to disseminate the level of short term purge compensation (i.e., the tactical error term) into the appropriate source (canister loading or tank flow rate) is made possible without losing control stability.
The strategic adaption routine is performed to direct the tactical error term to a canister model for learning canister loading or to a fuel tank model for learning tank vapor flow rates. The strategic adaption routine also combines the tactical error term and the contribution from the canister and fuel tank models to yield a total purge concentration at the manifold.
The canister model uses the output of the stra
Coatesworth Timothy A.
Duty Mark J.
Ohl Gregory L.
Sanyal Amit K.
Calcaterra Mark P.
Castro Arnold
DaimlerChrysler Corporation
Yuen Henry C.
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