Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
2000-01-11
2001-08-14
Solis, Erick (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C123S327000, C123S361000, C123S399000, C123S492000, C123S493000
Reexamination Certificate
active
06273060
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system and method for controlling an internal combustion engine coupled to an emission control device.
BACKGROUND OF THE INVENTION
In port fuel injected engines operating with a three way catalytic converter, it is desired to maintain near stoichiometric conditions during most operating conditions. Such control is especially difficult during transient conditions where airflow is rapidly changing. Any significant deviations from stoichiometry, either rich or lean of stoichiometry, are outside the operating window of the three way catalytic converter and tend to degrade emission performance. Thus, various methods have been used to improve air-fuel ratio control.
A common approach to improve air-fuel control is to use a so called transient fuel algorithm as is known to those skilled in the art. In this approach, fueling delays and fuel storage (puddling) in the intake manifold are taken into consideration when controlling fuel injectors. In other words, these transient fuel algorithms account for fuel supplied from both fuel injectors and from the manifold fuel puddle to the cylinder.
Continuing with this approach, a desired cylinder fuel amount is found from measured or estimated cylinder air charge. Then, the desired cylinder fuel amount is used to calculate a required fuel injection amount, taking manifold fuel puddling into consideration.
Finally, the required fuel injection amount is used to calculate an injector pulse width, or opening duration. In this way, air-fuel ratio can be more accurately controlled to stoichiometric conditions. Such a system is described in U.S. Pat. No. 5,746,183.
It is also known to control airflow to provide a desired engine torque. In certain conditions, such as during tip-out conditions where a vehicle operator removes their foot from the accelerator pedal, it might be desirable to rapidly reduce engine airflow to rapidly reduce engine torque.
The inventors herein have recognized a disadvantage with known approaches for controlling air-fuel ratio with transient fuel algorithms during such rapid airflow transients. In particular, during these tip-out situations, transient fuel algorithms determine that fuel needs to be taken out of the intake ports since excessive fuel is being supplied by the manifold fuel puddle. However, such action is not possible since conventional fuel injectors can only inject fuel into the intake ports. Therefore, the best that the fuel injectors can perform is to inject no fuel. As a result, a rich excursion occurs and emission performance is degraded. In other words, even when no fuel is injected by fuel injectors, fuel in excess of the stoichiometric ratio is inducted from the manifold fuel puddle into the cylinder.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide a method for controlling fuel injection and airflow wherein improved emission control is achieved.
The above object is achieved, and disadvantages of prior approaches overcome, by a control method for an internal combustion engine having at least one cylinder, the engine combusting a mixture of air and fuel in the at least one cylinder, the engine coupled to a first control device and a second control device. The method comprises determining a desired value of an engine operating parameter, wherein said operating parameter is affected by a first variable and a second variable, wherein said first variable is controlled by the first control device and said second variable is controlled by the second control device, and controlling said operating parameter to said desired value by adjusting said first control device when said second control device is at an operational limit.
By recognizing that there is a minimum possible fueling control, it is possible to control air when fuel control reaches this minimum limit, thereby maintaining robust air-fuel control. For example, in one embodiment of the present invention, during tip-out conditions where it is desired to rapidly reduce engine torque while maintaining stoichiometric conditions, airflow is allowed to rapidly decrease until fuel injection timing reaches a lower threshold, which could be zero. After this, airflow is limited so that required fuel injection timing stays within acceptable limits.
Similarly, there is a maximum fuel control on tip-ins that can be achieved. Again, by recognizing this maximum limit, airflow can be used to maintain a desired air-fuel ratio.
An advantage of the above aspect of the present invention is improved air-fuel control.
Another advantage of the above aspect of the present invention is improved air-fuel control during tip-out conditions.
In an alternate embodiment, the above object is achieved and disadvantages of prior approaches overcome by a method for controlling an internal combustion engine having at least one cylinder communicating with an intake manifold, the intake manifold coupled to an airflow control device, the airflow control device for adjusting an airflow, the engine also coupled to a fuel injector. The method comprises determining a minimum achievable fuel flow into the cylinder, calculating a minimum desired airflow based on said minimum achievable fuel flow into the cylinder, and controlling the airflow control device to provide at least said minimum desired airflow.
By controlling airflow so that that at least the airflow needed to maintain a desired air-fuel ratio at the minimum allowing fuel injection amount, rich excursions during tip-out conditions are avoided.
An advantage of the above aspect of the present invention is improved air-fuel control.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Buckert John
Ford Global Technologies Inc.
Solis Erick
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