Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2000-04-14
2001-08-28
Wolfe, Willis R. (Department: 2857)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C701S103000, C073S118040, C123S478000
Reexamination Certificate
active
06282485
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an estimation method for estimating an air quantity entering the cylinder of an internal combustion engine where a throttle mass air flow signal is used.
BACKGROUND OF THE INVENTION
Engine control systems require accurate control of the air/fuel ratio for controlling regulated emissions. In addition fuel economy improvements from operating the engine in the lean region also require precise air/fuel ratio control. For precise air/fuel control, an open loop estimate of the air entering the engine is required due to the delayed exhaust sensor response. The open loop estimate of air entering the cylinder, or cylinder air charge, is a particular problem when using a mass air flow sensor. The problem is due to the manifold volume, which tends to add dynamics that separate the air measured at the throttle body by the mass air flow sensor and from air inducted into the cylinder.
One approach to estimating the cylinder air charge is to use a first order difference equation that represents the manifold dynamics. In this system, the difference equation parameter, or filter parameter, is a function of volumetric efficiency, which is in turn a function of atmospheric conditions. For example, the filter parameter is a function of barometric pressure and air temperature. Each of these parameters is constantly monitored and used to recalculate the filter parameter during every operation of the estimation method. In addition the difference equation uses past parameters, thus requiring intermediate parameter storage. Such a system is described in U.S. Pat. No. 5,331,936.
The inventors herein have recognized a disadvantage with the above system. The nature of the difference equation requires extensive testing and parameter mapping across many conditions, such as, for example, changes in barometric pressure and air temperature. As a result, calibration effort of such an estimation scheme is greater than necessary. In addition because the parameter values are functions of many other parameters, extensive computation power is required for performing all of the necessary computations. Further, past parameter storage requires additional memory and computer operation time.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide a method for estimating an air quantity entering a cylinder of an internal combustion engine having a manifold and an air flow sensor coupled to the manifold. The method comprises the steps of measuring a quantity of air entering the manifold based on the air flow sensor, calculating a first filter parameter independent of ambient conditions, said first filter parameter based on a manifold volume, a number of cylinders, a displacement volume, and a stored slope of a graph between manifold pressure and air quantity entering any one of the cylinders, calculating a second filter parameter as one minus said first filter parameter, and estimating the air quantity entering the cylinder based on said measured air quantity entering the manifold, said first filter parameter, and said second filter parameter.
By estimating the air quantity entering the cylinder based on the air entering the manifold and using a first order difference equation with a filter parameter suitably calculated solely as a function independent of ambient operating conditions, such as, for example, as a function of a stored slope of a graph between manifold pressure and cylinder air charge, it is possible to obtain a more accurate estimation than prior art estimation. In addition, by performing the estimation in this way, complex calculations for determining the effect of unnecessary parameters, such as, for example, barometric pressure and gas temperature, are not required. In other words, prior art has used the term volumetric efficiency as a parameter in air charge estimation systems. Since volumetric efficiency is a function of barometric pressure, temperature and several other factors, to obtain an accurate estimate, all of these factors must be included. In the present invention, an alternate formulation is used in which volumetric efficiency is dissected. This removes the dependencies on barometric pressure, temperature, etc., resulting in a simple and more accurate estimation scheme. Further, because the present invention provides a simpler estimation scheme, calibration efforts are significantly reduced. Also, computation time and memory can be reduced because of the reduced complexity.
An advantage of the above aspect of the invention is increased air charge estimation.
Another, more specific, advantage of the present inventions is improved emission control.
Another advantage of the above aspect of the invention is reduced calibration cost.
Yet another advantage of the above aspect of the invention is reduced system cost.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Kotwicki Allan Joseph
Lewis Donald J.
Pursifull Ross Dykstra
Russell John David
Ford Global Technologies Inc.
Lippa Allan J.
Wolfe Willis R.
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