Variable valve control apparatus

1. A variable valve control apparatus comprising:

a variable valve actuating mechanism arranged to vary a closing timing of an intake valve; and

a controller configured

to advance the closing timing of the intake valve before a bottom dead center of a piston of an intake stroke until a load of an engine increases from a minimum load to a predetermined load, and

to retard the closing timing of the intake valve from a timing before the bottom dead center of the piston, to a timing after the bottom dead center of the piston when the load becomes the predetermined load.

2. The variable valve control apparatus as claimed in claim 1 , wherein the controller is configured to advance the closing timing of the intake valve closer to the bottom dead center of the piston when the load further increases beyond the predetermined load after the closing timing of the intake valve becomes the timing after the bottom dead center of the piston.

3. The control apparatus as claimed in claim 1 , wherein the variable valve actuating mechanism is arranged to vary an operation angle and a lift quantity of the intake valve.

4. The variable valve control apparatus as claimed in claim 1 , wherein the variable valve actuating mechanism is arranged to continuously vary the closing timing of the intake valve; and the controller is configured to continuously retard the closing timing of the intake valve closer to the bottom dead center of the piston from the timing before the bottom dead center of the piston until the load of the engine increases from the minimum load to the predetermined load.

5. The variable valve control apparatus as claimed in claim 4 , wherein the controller is configured to continuously advance the closing timing of the intake valve closer to the bottom dead center of the piston when the load further increases beyond the predetermined load after the closing timing of the intake valve becomes the timing after the bottom dead center of the piston.

6. The variable valve control apparatus as claimed in claim 5 , wherein a rate of change of the closing timing of the intake valve at the predetermined load is larger than a rate of change of the closing timing of the intake valve at a load other than the predetermined load.

7. The variable valve control apparatus as claimed in claim 6 , wherein the controller is configured to control so that a time period from the bottom dead center of the piston to the closing timing of the intake valve when the load becomes the predetermined load is longer than a time period from the closing timing of the intake valve to the bottom dead center of the piston immediately before the load becomes the predetermined load.

8. The variable valve control apparatus as claimed in claim 6 , wherein the controller is configured to control so that a time period from the closing timing of the intake valve to the bottom dead center of the piston immediately before the load becomes the predetermined load is substantially identical to a time period from the bottom dead center of the piston to the closing timing of the intake valve when the load becomes the predetermined load.

9. The variable valve control apparatus as claimed in claim 1 , wherein there is provided a hysteresis between the predetermined load and a load at which the closing timing of the intake valve starts to advance when the load decreases from the load beyond the predetermined load.

10. The variable valve control apparatus as claimed in claim 1 , wherein the variable valve actuating mechanism is arranged to vary a closing timing of an exhaust valve; and the controller is configured to retard the closing timing of the exhaust valve, from a timing near the top dead center of the piston of the exhaust stroke when the load becomes the predetermined load.

11. The variable valve control apparatus as claimed in claim 1 , wherein the controller is configured to decrease a transient torque of the engine when the load becomes the predetermined load and the closing timing of the intake valve is varied from the timing before the bottom dead center of the piston, to the timing after the bottom dead center of the piston.

12. The variable valve control apparatus as claimed in claim 11 , wherein the controller is configured to decrease the transient torque of the engine by decreasing a fuel supply quantity to a combustion chamber of the engine.

13. The variable valve control apparatus as claimed in claim 11 , wherein the controller is configured to decrease the transient torque of the engine by retarding an ignition timing.

14. The variable valve control apparatus as claimed in claim 11 , wherein the controller is configured to decrease the transient torque of the engine by increasing an internal EGR of the engine.

15. The variable valve control apparatus as claimed in claim 11 , wherein the controller is configured to decrease the transient torque of the engine by decreasing a throttle opening.

16. A variable valve control apparatus comprising:

a variable valve actuating mechanism arranged to vary a closing timing of an intake valve; and

a controller configured

to advance the closing timing of the intake valve before a bottom dead center of a piston of an intake stroke when a variation of an accelerator opening is smaller than a predetermined quantity, and

to retard the closing timing of the intake valve from a timing before the bottom dead center of the piston, to a timing after the bottom dead center of the piston when the variation of the accelerator opening becomes equal to or greater than the predetermined quantity.

17. A variable valve control apparatus comprising:

a variable valve actuating mechanism arranged to vary a closing timing of an intake valve; and

a controller configured

to advance the closing timing of the intake valve before a bottom dead center of a piston of an intake stroke when a variation of an intake air is smaller than a predetermined quantity, and

to retard the closing timing of the intake valve from a timing before the bottom dead center of the piston, to a timing after the bottom dead center of the piston when the variation of the intake air becomes equal to or greater than the predetermined quantity.

18. A variable valve control apparatus comprising:

a variable valve actuating mechanism arranged to vary a closing timing of an intake valve; and

a controller configured

to vary, in a first control state, the closing timing of the intake valve closer to a bottom dead center of a piston of an intake stroke until a load of an engine increases from a minimum load to a predetermined load,

to suddenly vary, in a second control state, the closing timing of the intake valve from a timing before the bottom dead center of the piston, to a timing after the bottom dead center of the piston by a variation speed greater than a variation speed in the first control state when the load becomes exceeds the predetermined load, and

to gently vary, in a third state, the closing timing of the intake valve closer to the bottom dead center of the piston by a variation speed smaller than the speed in the second control state when the load further increases beyond the predetermined load.

19. The variable valve control apparatus as claimed in claim 18 , wherein the controller is configured to control a throttle opening in the first control state to a large opening degree in the first control state, and to control a throttle opening in the third control state to the large opening degree substantially identical to the large opening degree in the first control state.

20. The variable valve control apparatus as claimed in claim 18 , wherein the variable valve actuating mechanism includes a first variable valve actuating mechanism arranged to continuously vary an operation angle of the intake valve, and a second variable valve actuating mechanism arranged to continuously vary a lift phase of the intake valve.