1. Field of the Invention
The present invention relates to a control apparatus of an engine having a variable valve lift apparatus and a method thereof. More particularly, the present invention relates to a control apparatus of an engine having a variable valve lift apparatus and a method for constantly maintaining pressure of a cylinder by driving an intake valve or an exhaust valve in a low lift mode when a cylinder is in an idle state.
2. Description of Related Art
In general, an internal combustion engine generates power by taking in fuel and air and burning it in a combustion chamber. Intake valves are operated by a camshaft in order to take in air, and air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and exhaust gas is discharged from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on the rotation speed of the engine. That is, an optimal lift or an optimal opening/closing timing of the valves depends on the rotation speed of the engine. In order to achieve such optimal valve operation depending on the rotation speed of the engine, research has been undertaken for a variable valve lift (VVL) apparatus that includes a plurality of cams for driving the valves, or varies the lift of the valves depending on the number of rotations per minute of the engine.
In a similar concept to the VVL apparatus, there is a CDA device. In general, cylinder deactivation (hereafter referred to as CDA) is a technology of deactivating some cylinders when braking or driving at a predetermined speed. During the operation of the CDA device, fuel supply to the deactivated cylinders is stopped and the operation of the intake/exhaust valves is stopped.
When a cylinder is deactivated, the intake valve and the exhaust valve are both closed, and an explosive gas or intake air is trapped in the cylinder. When the explosive gas or intake air is trapped in the cylinder, as shown in FIG. 1 (refer to arrow), there is a problem that an impact or a vibration is generated by a rapid increment of pressure in the cylinder at an initial state of cylinder deactivation.
As time passes, the pressure leaks outside of the cylinder, and thus negative pressure is formed in the cylinder. Therefore, oil flows into the cylinder.
Further, since the pressure in the cylinder is recovered to an original state when the cylinder is activated, there is a problem that fuel consumption is deteriorated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the related art already known to a person skilled in the art.