Variable valve timing controller for an engine

1. A variable valve timing controller for controlling operation of an intake-valve and an exhaust-valve equipped with an engine, comprising:

a valve-over-lap setting controller for setting an operation mode for lift timing of said intake-valve and exhaust-valve; and

a variable valve timing mechanism controller for operating said intake-valve and said exhaust-valve individually according to the operation mode set by said valve-over-lap setting controller, wherein

said valve-over-lap setting controller sets the operation mode to a first mode when the engine is just started, and

if a first predetermined condition is met after the first mode is set then

said valve-over-lap setting controller resets the operation mode from the first mode to a second mode,

wherein, said valve-over-lap setting controller sets the first mode, which instructs said variable valve timing mechanism controller so that at least one-half of a period, from the closing time of said exhaust-valve to the opening time of said intake-valve, is set during an exhaust stroke of the engine.

2. The variable valve timing controller as set forth in claim 1 , wherein, in the first mode, said valve-over-lap setting controller instructs said variable valve timing mechanism controller operating, such that said intake-valve is opened at the top dead center.

3. The variable valve timing controller as set forth in claim 1 , wherein, in the second mode, said valve-over-lap setting controller instructs said variable valve timing mechanism controller, such that the closing time of said exhaust-valve and the opening time of said intake-valve are the same.

4. The variable valve timing controller as set forth in claim 1 , wherein, in the first mode and the second mode, an air/fuel ratio is set to a stoichiometric ratio and an ignition timing is retarded.

5. The variable valve timing controller as set forth in claim 1 , wherein the first predetermined condition is a predetermined time after start of an engine.

6. The variable valve timing controller as set forth in claim 1 , wherein the first predetermined condition is a predetermined time after start of an engine under a cold condition.

7. The variable valve timing controller as set forth in claim 1 , wherein, when a second predetermined condition is met during said second mode, said valve-over-lap setting controller sets a third mode which instructs said variable valve timing mechanism controller, such that the closing timing of said exhaust-valve is shifted to a timing after the top dead center.

8. The variable valve timing controller as set forth in claim 7 , wherein the second predetermined condition is one of a predetermined time after a start of the second mode, a revolution speed of the engine reaches a predetermined revolution speed, and a vehicle speed reaches a predetermined speed.