Cam Profile Switching (CPS) technology has significant effect on drivability, exhaust emissions and fuel consumption. New legislative requirements for the exhaust gas emissions regulations imposed recently by the State of California and the Environmental Protection Agency demand the ability to conduct a continuous monitoring of the state of CPS (Cam Profile Switching System). This, in its turn, requires to have an effective diagnostic method for identification of the system failure. The valve lift event can not be directly measured and special diagnostic algorithms, based on indirect information about the valve lift, are required to identify a failure in the system.
Several methods which allow detecting the CPS state are known. The first one is based on the difference in the air charge inducted in the cylinders for different lifts. The inducted air charge measured by Manifold Air Flow (MAF) sensor is compared with the air charge model based on the measured position of the throttle flap, intake manifold pressure and engine speed. The CPS state is associated with the error between measured and modelled air charge,
The drawback of the method described in US 6213 068 is that the method does not allow the cylinder individual failure detection. It is furthermore not suitable for the detection of the failure of a one bank either due to the relatively small difference in volumetric efficiency for the case of a single Bank failure.
Another method is based on the combustion state monitoring using fluctuations of the engine speed. The method is based on the fact that the combustion state changes considerably during shifting, US 6 006 152. The invention uses the technique of the combustion state monitoring via irregularities of the engine speed. Irregularities are associated with the CPS state. The method allows the cylinder individual failure detection. The method uses the torque estimation technique which is well known in the literature devoted to the combustion efficiency monitoring functions.
Another group of methods proposes to associate the CPS state with the fluctuations of the intake manifold pressure signal. The closest invention which proposes to recover the intake valve timing information from the pressure signal is disclosed in the US 5495830. The method for control and monitoring of the check valves is described in US 5495830. Intake valve closing events which are determined via the pressure change allow to estimate an amount of the backflow into the intake runner where the check valve is controlled to minimize the backflow effect. To realize the algorithms proposed in the US 5495830 the pressure sensor is required in every intake passage which increases the cost of the system.
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