Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2002-11-19
2004-04-13
Denton, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090150, C123S090110, C701S102000
Reexamination Certificate
active
06718922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a cam phase control for an internal combustion engine, and more particularly, to a cam phase control apparatus and method, and an engine control unit for an internal combustion engine which rely on a response specifying control algorithm to control an actual cam phase of an intake cam and/or exhaust cam with respect to a crank shaft to converge the actual cam phase to a target cam phase.
2. Description of the Prior Art
A conventional cam phase control apparatus of the type mentioned above is known, for example, from Laid-open Japanese Patent Application No. 2001-132482. An internal combustion engine associated with the cam phase control apparatus comprises a cam phase varying device for changing an actual cam phase of an intake cam. The cam phase varying device comprises a hydraulically driven cam phase varying mechanism, an electromagnetic control valve for supplying the cam phase varying mechanism with an oil pressure from an oil pump, and the like. The cam phase control apparatus in turn comprises a crank angle sensor and a cam angle sensor for detecting signals corresponding to angular positions of a crank shaft and an intake cam, respectively, and a controller which receives the signals detected by these sensors. The controller calculates an actual cam phase based on the signals detected by the crank angle sensor and cam angle sensor, calculates a target cam phase based on an operating condition of the internal combustion engine, and controls the actual cam phase to converge to the target cam phase based on a sliding mode control algorithm which is one type of the response specifying control algorithm.
Specifically, the sliding mode control algorithm models, as a continuous time based model, a controlled object which includes the cam phase varying mechanism and the electromagnetic control valve, and receives a control input to the electromagnetic control valve and outputs a calculated actual cam phase. More specifically, a state equation representative of the controlled object is set as a differential equation which has state variables that represent a first and a second time derivative value of the actual cam phase. A switching function is additionally set as a linear function which has a state variable that represents a deviation of the actual cam phase from the target cam phase, and a time-derivative value (i.e., a changing rate) of the deviation. Then, a control input is calculated such that the deviation and changing rate thereof represented by the state variables of the switching function set in the foregoing manner rest on a switching line, i.e., the control input is calculated such that the deviation and changing rate thereof slide on the switching line to converge to zero, thereby controlling the actual cam phase to converge to the target cam phase.
Generally, the hydraulically driven cam phase varying mechanism exhibits an intense friction characteristic, so that the conventional cam phase varying device preferably controls such a controlled object at a control period as short as possible from a viewpoint of improving the controllability. In addition, since the target cam phase is calculated based on an operating condition of the internal combustion engine, its power spectrum exists in a much lower frequency region than the frequency corresponding to the control period. This means that since the target cam phase is calculated based on a parameter such as the operating condition, accelerator opening, or the like, which changes at a low rate, the calculated target cam phase also changes at a low rate.
Therefore, in the conventional cam phase control apparatus which employs a changing rate of the deviation of the actual cam phase from the target cam phase as a state variable of the switching function, the target cam phase changing at a low rate causes a slow changing rate of the actual cam phase which is controlled based on the target cam phase, so that the changing rate of the deviation of the actual cam phase from the target cam phase lies in the vicinity of zero, if detected at short time intervals such as the control period, meaning that the deviation will remain unchanged. As a result, the calculated deviation is susceptible to noise, and therefore suffers from a low calculation accuracy. Further, the changing rate of the deviation lies in the vicinity of zero so that the switching function is substantially equivalent to the deviation, resulting in a failure in ensuring the robustness and response specifying characteristic due to difficulties in implementing a sliding mode which is unique to the sliding mode control. From the foregoing, the conventional cam phase control apparatus can fall into low controllability in a transient state in which the actual cam phase converges to the target cam phase, possibly causing the actual cam phase to overshoot the target cam phase, by way of example.
Also, since the conventional cam phase control apparatus models a controlled object as a continuous time based model, it is difficult to directly identify model parameters of the controlled object from data derived from an experiment on the controlled object. For this reason, specifically, the continuous time based model must be approximately converted to a discrete time based model to identify the model parameters based on the approximate conversion. However, the use of such an approximation conversion will cause a degraded identification accuracy of the model parameters. Furthermore, since the discrete time based model is again approximately converted to a continuous time based model, increased modeling errors will introduce into the controlled object model due to the “round-trip” approximation conversions. Consequently, a controller gain must be limited for ensuring a margin for control stability, resulting in degraded controllability.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made to solve the problems mentioned above, and it is an object of the invention to provide a cam phase control apparatus and method, and an engine control unit for an internal combustion engine which are capable of improving the controllability in a transient state in which an actual cam phase converges to a target cam phase to accurately and readily identify model parameters even when a mechanism for changing the actual cam phase exhibits an intense friction characteristic.
To achieve the above object, according to a first aspect of the present invention, there is provided a cam phase control apparatus for an internal combustion engine for controlling an actual cam phase of at least one of an intake cam and an exhaust cam with respect to a crank shaft.
The cam phase control apparatus according to the first aspect of the present invention is characterized by comprising cam phase varying means for changing the actual cam phase; cam phase detecting means for detecting the actual cam phase; operating condition detecting means for detecting an operating condition of the internal combustion engine; target cam phase setting means for setting a target cam phase in accordance with the detected operating condition; and control means relying on a response specifying control algorithm to determine a control input to the cam phase varying means at a predetermined control period for converging the actual cam phase to the target cam phase, wherein the response specifying control algorithm is configured to model a controlled object which receives the control input to the cam phase varying means and outputs the actual cam phase, and the controlled object is represented by a discrete time based model.
According to this cam phase control apparatus for an internal combustion engine, since the controlled object is modeled as a discrete time based model in the response specifying control algorithm, model parameters can be more accurately and readily identified in accordance with a general identification algorithm such as a least square method based on data obtained from experiments and simulations t
Denton Thomas
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Laurentano Anthony A.
Riddle Kyle
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