| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable-valve timing device, capable of surely suppressing discharging of unburned HC by properly controlling the opening and closing timings of intake and exhaust valves at the time of cold starting SOLUTION: At the beginning of cold start, when an exhaust passage has yet to be sufficiently heated and afterburning effect cannot be expected, overlapping amount is increased (2, 3). As a result of this, the exhaust gas once passed through to the exhaust side is returned into a cylinder and burned to suppress the discharge of unburned HC, and the exhaust gas is allowed to make reverse flow in the intake side, to realize promotion of the vaporization of fuel and the temperature rise of the intake port. Then, when the exhaust passage is heated (4), the exhaust valve is spark-advanced to discharge the exhaust gas during combustion, and catalyst is activated earlier by the afterburning effect in the exhaust passage. |
