1. Field of the Invention
The invention relates to a multicylinder engine in which part of cylinders may be deactivated, and a method for controlling the same.
2. Description of the Related Art
Multicylinder engines of this type are described in, for example, Japanese Patent Application Publication No. 07-217461 (JP-A-07-217461), Japanese Patent Application Publication No. 2004-300994 (JP-A-2004-300994), Japanese Patent Application Publication No. 2007-15653 (JP-A-2007-15653), Japanese Patent Application Publication No. 2007-23793 (JP-A-2007-23793), and Japanese Patent Application Publication No. 2007-162606 (JP-A-2007-162606). In this type of engine, the vibration developmental state differs between normal engine operation and cylinder deactivation. Therefore, measures need to be taken to control vibration and noise. JP-A-07-217461 and JP-A-2007-15653 suggest the following measures. According to JP-A-07-217461, the characteristics of a mount that supports the engine are made different between normal engine operation and cylinder deactivation. According to JP-A-2007-15653, the vibration developmental state is estimated based on the angular acceleration of a crankshaft, and the operation of an actuator provided in an active vibration-proofing support member that supports the engine is controlled based on the estimated vibration developmental state.
Ignition/combustion may take place in operating cylinders at uneven intervals in some cylinder deactivation modes (e.g. in virtual V-four engine operation mode in which two cylinders are deactivated in a V-six engine). In this case, the output torque may vary between the operating cylinders, which are immediately subsequent to deactivated cylinders in the firing order, and the other operating cylinders (refer to “problems to be solved by the invention” in JP-A-2007-162606). Therefore, during cylinder deactivation where combustion takes place in the operating cylinders at uneven intervals, vibration and noise may increase.
Accordingly, the above-described active vibration-proofing support member may be used to suppress vibration and noise. However, the actual vibration developmental state is complicated by the above-described output torque variation among the operating cylinders. Accordingly, it is difficult to accurately estimate the vibration developmental state. If the active vibration-proofing support member is controlled based on the result of inaccurate estimation of the vibration developmental state, vibration and noise are not suppressed at a sufficient level. Instead, vibration and noise may increase.