Engine equipped with adjustable valve timing mechanism

1. An engine equipped with an adjustable valve timing mechanism, comprising:

an inlet valve opening term varying mechanism, which is included in said adjustable valve timing mechanism, varying an opening term of an inlet valve; and

an inlet valve opening term controller controlling said inlet valve opening term varying mechanism according to a running state of the engine,

said inlet valve opening term controller setting the opening term of the inlet valve to a first inlet term when the engine runs at a predetermined high load and a predetermined high speed,

said inlet valve opening term controller also setting the opening term of the inlet valve to a second inlet term

which is longer than the first inlet term,

which has a starting timing of the inlet valve opening retarded compared to the starting timing of the inlet valve opening in the first inlet term, and

has a termination timing of the inlet valve opening in the second inlet term retarded compared to the termination timing of the inlet valve opening in the first inlet term, when the engine runs at a predetermined low load, lower than the predetermined high load, and a predetermined low speed, slower than the predetermined high speed.

2. The engine equipped with the adjustable valve timing mechanism according to claim 1 , wherein

said inlet valve opening term controller sets the opening term of the inlet valve to a third inlet term which is shorter than the first inlet term and which has a termination timing of the inlet valve opening advanced compared to the termination timing of the inlet valve opening in the first inlet term, when the engine runs at the predetermined high load and the predetermined low speed.

3. The engine equipped with the adjustable valve timing mechanism according to claim 2 , wherein

said inlet valve opening term controller sets the termination timing of the inlet valve opening in a latter half of a compression stroke when the engine runs at the predetermined low load and the predetermined low speed.

4. The engine equipped with the adjustable valve timing mechanism according to claim 3 , wherein

said inlet valve opening term controller sets the opening term of the inlet valve to a fourth inlet term shorter than the second inlet term, when the engine runs at maximum power.

5. The engine equipped with the adjustable valve timing mechanism according to claim 3 , wherein

said inlet valve opening term controller sets the termination timing of the inlet valve opening in a former half of the compression stroke when the engine is started.

6. The engine equipped with the adjustable valve timing mechanism according to claim 5 , wherein

said inlet valve opening term controller sets the opening term of the inlet valve to a fourth inlet term shorter than the second inlet term, when the engine runs at maximum power.

7. The engine equipped with the adjustable valve timing mechanism according to claim 2 , further comprising:

an inlet characteristic phase shifting mechanism, included in said inlet valve timing mechanism, shifting a phase of a valve lifting characteristic of the inlet valve; and

an inlet characteristic phase controller controlling said inlet characteristic phase shifting mechanism, wherein

said inlet characteristic phase controller sets the phase of the valve lifting characteristic to a first inlet phase when the engine runs at the predetermined high load,

said inlet characteristic phase controller also sets the phase of the valve lifting characteristic to a second inlet phase, which is retarded compared to said first inlet phase, when the engine runs at the predetermined low load and the predetermined low speed.

8. The engine equipped with the adjustable valve timing mechanism according to claim 7 , wherein

said inlet characteristic phase controller sets the phase of the valve lifting characteristic to a third inlet phase, which is advanced compared to said first inlet phase, when the engine runs at the predetermined high load and the predetermined low speed.

9. The engine equipped with the adjustable valve timing mechanism according to claim 8 , wherein

said inlet valve opening term controller and said inlet characteristic phase controller set the phase of the valve lifting characteristic of the inlet valve so that the starting timing of the inlet valve opening is in proximity to the starting timing of an inlet stroke, when the engine runs at the predetermined low load and the predetermined low speed.

10. The engine equipped with the adjustable valve timing mechanism according to claim 9 , wherein

said inlet valve opening term controller sets the opening term of the inlet valve to a fourth inlet term shorter than the second inlet term, when the engine runs at maximum power.

11. The engine equipped with the adjustable valve timing mechanism according to claim 8 , wherein

said inlet valve opening term controller and said inlet characteristic phase controller set the phase of the valve lifting characteristic to make an overlap term, during which both the inlet valve and an exhaust valve are opening, to a first overlap term, when the engine runs at the predetermined high load and the predetermined high speed,

said inlet valve opening term controller and said inlet characteristic phase controller also set the overlap term to a second overlap term, which is longer than the first overlap term, when the engine runs at the predetermined low load and the predetermined low speed.

12. The engine equipped with the adjustable valve timing mechanism according to claim 11 , wherein

said inlet valve opening term controller and said inlet characteristic phase controller set the overlap term to a fourth overlap term which is longer than the second overlap term, when the engine runs at maximum power.

13. The engine equipped with the adjustable valve timing mechanism according to claim 7 , wherein

said inlet valve opening term controller and said inlet characteristic phase controller set the phase of the valve lifting characteristic of the inlet valve so that the starting timing of the inlet valve opening is in proximity to the starting timing of an inlet stroke, when the engine runs at the predetermined low load and the predetermined low speed.

14. The engine equipped with the adjustable valve liming mechanism according to claim 13 , wherein

said inlet valve opening term controller sets the opening term of the inlet valve to a fourth inlet term shorter than the second inlet term, when the engine runs at maximum power.

15. The engine equipped with the adjustable valve timing mechanism according to claim 7 , wherein

said inlet valve opening term controller and said inlet characteristic phase controller set the phase of the valve lifting characteristic to make an overlap term, during which both the inlet valve and an exhaust valve are opening, to a first overlap term, when the engine runs at the predetermined high load and the predetermined high speed,

said inlet valve opening term controller and said inlet characteristic phase controller also set the overlap term to a second overlap term, which is longer than the first overlap term, when the engine runs at the predetermined low load and the predetermined low speed.

16. The engine equipped with the adjustable valve timing mechanism according to claim 15 , wherein

said inlet valve opening term controller and said inlet characteristic phase controller set the overlap term to a fourth overlap term which is longer than the second overlap term, when the engine runs at maximum power.