Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2001-04-20
2003-07-08
Vo, Hieu T. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C060S276000, C123S694000, C701S108000, C701S109000
Reexamination Certificate
active
06591183
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-126281 filed on Apr. 21, 2000, 2000-179359 file on Jun. 9, 2000, 2000-404671 filed on Dec. 28, 2000, 2000-404672 filed on Dec. 28, 2000, and 2000-404694 filed on Dec. 28, 2000.
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, for feedback controlling an input of a subject to be controlled in an internal combustion engine.
2. Description of Related Art
In a vehicle under advanced electronic control in recent years, various controls are performed by feedback controls. For example, the feedback control is used for A/F ratio control (fuel injection control), variable valve timing control, electronic throttle control, fuel pump control, boost pressure control of a turbo charger, idle speed control, cruise control, and the like.
A conventional feedback control is carried out in such a manner that an output (controlled variable) of a subject to be controlled is detected by a sensor or the like, a correction amount of an input (operation amount) of the control subject is calculated in accordance with a deviation between the output of the control subject and a target value so that the output of the control subject coincides with the target value, and the input of the control subject is corrected by the correction amount to make the output of the control subject follow the target value.
In many cases, a system as a subject of the feedback control in a vehicle has a long waste time (a large delay element) and, moreover, the waste time varies according to the engine operating conditions, deterioration with time in a control system, and the like. Consequently, the conventional feedback control is easily influenced by the variations in waste time. When a higher gain is set to increase the response, the feedback control becomes unstable, and there is the possibility that hunting occurs. In the conventional feedback control, it is therefore difficult to realize both higher gain (higher response) and stability. Moreover, there is a drawback such that the stability is apt to deteriorate due to an influence of an error in modeling of the control subject, and robustness is low.
A vehicle has a three-way catalyst in its exhaust pipe to treat exhaust gases. In order to increase catalytic conversion efficiency, it is necessary to control the concentration of an exhaust gas to be within a catalytic conversion window (about target A/F ratio). An exhaust gas sensor (A/F ratio sensor or oxygen sensor) is disposed on each of the upstream and downstream sides of a catalyst, a fuel injection amount is feedback controlled so that the A/F ratio of an exhaust gas detected by the exhaust gas sensor on the upstream side is equal to an upstream-side target A/F ratio, and a sub-feedback control is performed to correct the upstream-side target A/F ratio so that the A/F ratio of the exhaust gas detected by the downstream-side exhaust gas sensor is equal to a downstream-side target A/F ratio.
The conventional sub-feedback control is performed by PID control. Recently, in order to increase control accuracy, as shown by the publication of JP-A-9-273439, a technique of using sliding mode control has been proposed. The sliding mode control relates to a feedback control method of a variable structure type of preliminarily building a hyperplane expressed by a linear function using a plurality of state variables of a subject to be controlled as variables, allowing a state variable to converge on the hyperplane by high gain control at high speed, and allowing the state variable to converge on a required equilibrium point on the hyperplane by an equivalent control input while restricting the state variable on the hyperplane.
Generally, the sliding mode control has an advantage that once the state variable of the control subject converges on the hyperplane, the state variable can stably converge on an equilibrium point on the hyperplane without almost no influence of disturbance or the like. However, only a mode of a subject to be controlled in the case where a state variable converges on a hyperplane is considered. Consequently, when the sliding mode control is applied to control the A/F ratio of exhaust gas as in the publication, generally, at a high gain, hunting occurs due to disturbances and waste time around the hyperplane, and a state such that the state variable does not converge on the hyperplane occurs. As shown in
FIG. 25
, an inconvenience such that an output of the downstream-side exhaust gas sensor (A/F ratio of the exhaust gas on the downstream side of the catalyst) does not converge on a target value (target A/F ratio on the downstream side) may occur depending on the initial states. On the other hand, at a low gain, there is a drawback such that an input is insufficient for an error in modeling, so that response deteriorates and, as shown in
FIG. 26
, the speed of convergence of an output of the downstream-side exhaust gas sensor (concentration of the exhaust gas on the downstream side of the catalyst) becomes conspicuously slow.
Further, as disclosed in Japanese Patent No. 2,518,247, it is proposed to increase an update amount of an exhaust gas A/F ratio feedback control constant (for example, a skip amount) as the deviation between an A/F ratio detected by the downstream-side exhaust gas sensor and the downstream-side target exhaust gas A/F ratio becomes larger.
Here, dynamic characteristics of a catalyst vary according to the degree of deterioration of the catalyst, catalytic conversion state, and engine operating conditions. However, it cannot be the that the response of sub feedback control of the conventional main/sub feedback system to a change in dynamic characteristics of a catalyst is sufficient. Consequently, there is the possibility that a delay occurs in the response of the sub feedback control to a change in dynamic characteristics of the catalyst, concentration of exhaust gas on the downstream side of the catalyst (output of the downstream-side exhaust gas sensor) becomes unstable, and hunting occurs.
A conventional feedback control is carried out in such a manner that an output (controlled variable) of a subject to be controlled is detected by a sensor or the like, a correction amount of an input (operation amount) of the control subject is calculated by proportional integral and derivative control (PID control) in accordance with a deviation between the output of the control subject and a target value so that the output of the control subject coincides with the target value, and the input of the control subject is corrected by the correction amount to make the output of the control subject follow the target value.
A correction amount calculated by a conventional feedback control using the PID control is derived by adding a proportional term, an integral term, and a differential term. Generally, in order to improve a start-up characteristic in the case where an output of a subject to be controlled follows a target value, it is effective to increase the gain of the differential term. It is presumed that, when the gain of the differential term is set to be too high, an influence of noise becomes large, overshoot occurs, and the performance of following the target value deteriorates. In the conventional feedback control, therefore, the gain of the differential term is set to be low and the gain of the proportional term is set to be high, thereby improving the performance of following the target value.
In various feedback controls regarding the engine control of a vehicle, however, a relatively large waste time and a phase delay exist in a subject to be controlled, and disturbance is large. Consequently, when the gain is increased to make response faster, the feedback control becomes unstable, and there is the possibility that hunting occurs. In the conventional feedback control, it is therefore difficult to realize both higher gain (higher response) and stabilit
Ishikawa Yosuke
Kawai Katsuhiko
Kita Masayuki
Denso Corporation
Nixon & Vanderhye P.C.
Vo Hieu T.
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