Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2000-10-19
2002-09-17
Kwon, John (Department: 3754)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C701S108000, C123S696000, C123S681000
Reexamination Certificate
active
06453229
ABSTRACT:
FIELD OF THE INVENTION
The preset invention relates to a device and method for carrying out an air-fuel ratio feedback control of an internal combustion engine, and more specifically, to a technology for carrying out a feedback control using a sliding mode control.
DESCRIPTION OF THE RELATED ART
It is common to carry out a feedback control for an internal combustion engine for vehicle, so as to approximate an air-fuel ratio to a target value, in order to improve the fuel consumption or the exhaust emission.
Therefore, while detecting the air-fuel ratio sequentially by an air-fuel ratio sensor equipped in an exhaust passage and the like, the fuel supply quantity is feedback controlled using PID control (proportional-integral-derivative), in order to converge the detected air-fuel ratio to the target air-fuel ratio.
On the other hand, a sliding mode control is known as a control method having high robust performance with suppressed influence from disturbance, which is often used in controlling robots and the like. A proposal is made to utilize the sliding mode control to the feedback control of the air-fuel ratio (Japanese Unexamined Patent Publication No. 8-232713).
However, the sliding mode control mentioned above used for the feedback control of the air-fuel ratio is not capable of eliminating the influence caused by the dispersion in the part performance for each engine, and therefore, was not highly accurate. This is because in designing the sliding mode control, the air-fuel ratio control system of the engine is modeled considering the response delay and the like of each part.
Moreover, the air-fuel ratio feedback control using the sliding mode control has a general problem. Since the air-fuel ratio is detected through a specific component in the exhaust, dead time, such as transfer delay of the exhaust and the like, exists between the air-fuel ratio detected from the exhaust and the actually controlled air-fuel ratio (fuel supply quantity). During such dead time, excessive compensation is performed. If such dead time is fixed, the computing cycle of the feedback control amount can be set corresponding to such a fixed dead time, to restrain excessive correction. However, the dead time greatly varies according to the operating conditions of the engine, and therefore, it was very difficult to set the computing cycle to an appropriate value. For example, if the computing cycle is set sufficiently large, excessive correction can be restrained, but the response characteristic is reduced. Actually, the computing cycle is set to be small to a certain extent to restrain excessive correction by keeping the feedback gain small. However, this deteriorates the response characteristic, and prevents the sliding mode control from performing its function sufficiently.
Heretofore, the sliding mode control utilized in the air-fuel ratio feedback control involves modeling and designing in detail the delay of various units in the air-fuel ratio control system including the above-mentioned dead time. Therefore, it involved extremely complicated and bothersome processes, could not be used generally for different types of vehicles or engines, and needed large capacity of ROM and RAM for carrying out the complicated control.
SUMMARY OF THE INVENTION
The present invention aims at solving the above mentioned problems. The object of the invention is to provide an air-fuel ratio feedback control using a highly accurate sliding mode control without no dispersion for each engine, that can be carried out easily, that is easy to design, and that can be generally applied to various types of vehicles and engines.
Another object of the invention is to ensure a good response characteristic while restraining excessive correction during dead time in an air-fuel ratio feedback control according to a sliding mode control.
Yet another object of the invention is to eliminate the influence of the dead time element existing in the control object without depending on the later correction of the feedback control amount, thereby ensuring the stability the response characteristic of the control system.
In order to achieve the first common object, the present invention includes the following basic constitution.
An air-fuel ratio is detected linearly by an air-fuel ratio sensor equipped for example in the exhaust passage.
A feedback control amount is computed according to a sliding mode control in which a deviation between a target air-fuel ratio set according to operating conditions of the engine and the detected air-fuel ratio is set as a switching function.
A feedback control is carried out using the computed feedback control amount, so as to approximate the detected air-fuel ratio to the target air-fuel ratio.
According to this constitution, the feedback control of the air-fuel ratio is carried out using the feedback control amount according to the sliding mode control in which the deviation (error) between the target air-fuel ratio and the detected air-fuel ratio (actual air-fuel ratio) is set as a switching function S. Thereby, the air-fuel ratio converges to the target air-fuel ratio while sliding along a switching plane defined as S=0 (in other words, error=0).
Here, the switching function S is set through a method called the direct switching function method of the sliding mode control. This method defines the switching plane (S=0) as a function representing the state to be achieved (in this case, to approximate the air-fuel ratio to the target air-fuel ratio). This method is characterized in that though there is no assurance that the state will slide on the switching plane, once the sliding is confirmed, it enables to provide the best sliding mode control. This is because the switching plane is decided based only on whether the target value is greater or smaller than the actual value, irrespective of a change in response characteristic of a fuel supply device or the air-fuel ratio sensor and the like.
When sliding mode control of the air-fuel ratio is carried out using the switching function set as explained above, it is confirmed that the air-fuel ratio slides along the switching plane.
Therefore, the feedback control according to the sliding mode control can be carried out easily and with high accuracy.
Moreover, unlike the conventional art, the present invention does not involve the complicated process of modeling the engine in order to set the switching function. Therefore, the present invention can be applied generally to different types of vehicle or engine.
Even further, the feedback control amount may include a linear term and a nonlinear term.
According to such a constitution, the feedback control amount computed by the sliding mode control comprises a linear term and a nonlinear term, the linear term adjusting the speed for approximating the state of the control system to the switching plane, and the nonlinear term generating the sliding mode along the switching plane.
Moreover, the linear term may be computed as a value proportional to the ratio between the deviation of the target air-fuel ratio and the detected air-fuel ratio to the detected air-fuel ratio.
According to this constitution, as the air-fuel ratio separates from the switching plane, in proportion to this separation, the linear term is set to a greater value, enabling the air-fuel ratio to approximate the switching plane promptly while suppressing overshooting.
Further, the nonlinear term may be computed by integrating a feedback gain, the positive or negative of which is switched according to whether the switching function is positive or negative.
According to this constitution, the positive or negative of the switching function will reverse whenever the state of the air-fuel ratio crosses the switching plane, and the positive or negative of the feedback gain will also reverse accordingly. By the nonlinear term computed by integrating the feedback gain, the air-fuel ratio promptly converges to the target air-fuel ratio while sliding along the switching plane.
Moreover, the absolute value of the feedback gain may be s
Hosoya Hajime
Iwaki Haruhiro
Ohkuma Shigeo
Takahashi Koji
Watanabe Satoru
Kwon John
Sughrue & Mion, PLLC
Unisia Jecs Corporation
Vo Hieu T.
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